Three hours to save Integral

Enabling & Support


On 22 September, round noon, ESA’s Integral spacecraft went into emergency Safe Mode. One of the spacecraft’s three lively ‘reaction wheels’ had turned off with out warning and stopped spinning, inflicting a ripple impact that meant the satellite tv for pc itself started to rotate.

As a results of the spacecraft turning, knowledge had been solely reaching floor management patchily and the batteries had been rapidly discharging. With just some hours of energy left, it appeared attainable that the 19-year-old mission could possibly be misplaced.The Integral Flight Control Team, along with Flight Dynamics and Ground Station Teams at ESA’s ESOC mission management, groups at ESAC and Airbus Defence & Space, set to work. With fast considering and ingenious options, they discovered the issue and rescued the mission.

What on Earth?

A Single Event Upset (SEU) happens when a charged particle strikes a delicate a part of electrical tools, inflicting a one-off ‘change of state’ that disrupts its functioning. These charged, ‘ionised’ particles typically come from the Sun when it spews out matter and power throughout photo voltaic flares or coronal mass ejections.

Three hours to save Integral – what occurred?

“I don’t think that the SEU on this occasion was caused by our local, occasionally grumpy star. This strike happened on a day when no relevant space weather activity was observed,” explains Juha-Pekka Luntama, ESA’s Head of Space Weather.“Based on a discussion with our colleagues in the Flight Control Team, it looks like that the anomaly was triggered by charged particles trapped in the radiation belts around Earth.”The Van Allen radiation belts are two doughnut-shaped areas encircling Earth, the place energetic charged particles are trapped inside Earth’s magnetic subject. Their properties range in accordance to photo voltaic exercise they usually characterize a hazard to satellites and people in area that move via them. Because the bottom level of Integral’s orbit is now solely 1500 km from Earth’s floor, the spacecraft passes via each radiation belts in its orbit.

‘Darmstadt, we have a problem’

Integral makes use of ‘reaction wheels’ – wheels that retailer power as they spin – to subtly management the path the spacecraft factors in with out the necessity of thrusters.Suddenly, one in all these response wheels stopped and, due to the legislation of conservation of power, that turning drive beforehand within the wheel had to go some place else – all the spacecraft. The spacecraft started to spin, triggering an Emergency Safe Attitude Mode which sadly, due to a earlier failure, was now not dependable and didn’t handle to stabilise the mission.

The Integral Flight Control Team set to work rescuing the mission

The response wheel was reactivated by groups on the bottom, however the spacecraft saved spinning at a mean price of about 17 levels per minute (roughly one rotation each 21 minutes), in addition to wobbling unpredictably about its axes. This could not sound like a lot, however the spacecraft was rotating at 5 instances its most when beneath management.“The data coming down from Integral was choppy, coming in for short periods due to it spinning. This made analysis even harder,” explains Richard Southworth, Operations Manager for the mission.“The batteries were discharging, as there were only short charging periods when the panels briefly faced the Sun.”The first problem was to lower Integral’s power consumption to purchase extra time. First estimates of the cost remaining earlier than blackout and the lack of the satellite tv for pc was simply three hours. Step by step, by turning off varied devices and non-critical parts, this elevated to greater than six hours. Next step – cease the spinning.With assist from business specialists, the group at ESOC analysed the state of the response wheels, developing with a collection of instructions to change their velocity and brake the spinning satellite tv for pc. By late afternoon, the instructions had been despatched and instantly confirmed success, however one other three lengthy hours handed earlier than the satellite tv for pc was totally beneath management and out of speedy hazard.

Integral’s ‘Apollo 13’ second

“Everyone breathed a huge sigh of relief. This was very close, and we were immensely relieved to get the spacecraft out of this ‘near-death’ experience,” remembers Andreas Rudolph, Head of the Astronomy Missions Division in ESOC’s Mission Operations Department.

An artist’s impression of the mechanisms in an interacting binary system

“Most of the Control Team were working from home at this point – I was following operations from the train! – and worked until four in the morning to get the spacecraft fully stable, back into position and facing the Sun to recharge its batteries.”Unfortunately, a couple of hours later because the group reconvened to talk about the following steps, the spacecraft as soon as once more began to rotate, its response wheels once more turning at excessive velocity. The motive for that is nonetheless not utterly understood however is assumed to be related to a ‘star tracker occultation’ or ‘blinding’ which wasn’t dealt with accurately by the satellite tv for pc’s management programs – successfully when Earth will get in the way in which of the spacecraft’s view of the celebs, which it makes use of to orient itself.The group repeated the earlier days steps to stabilise the spacecraft and return to a Sun pointing place, this time with out getting in the way in which of the star trackers. The restoration took simply a few hours, placing in to follow the teachings learnt from the primary time.

Hubble’s sharpest view of the Orion Nebula

Integral has since remained beneath management, and from 27 September all programs are again on-line. Since 1 October, after an prolonged checkout, its devices are again observing the excessive power Universe.One of the primary targets for Integral will likely be to observe large stars within the Orion area, and examine the affect on their environment once they go supernova.“We are also back to ‘target of opportunity’ observations, which means that Integral is again reacting quickly to study unexpected explosive events in the Universe,” says Erik Kuulkers, ESA’s Project Scientist for Integral.

An issue of thrust

It’s not the primary time this virtually 20-year-old mission gave the management group at ESA’s ESOC Operations Centre a scare. Last 12 months, Integral fired its thrusters for presumably the final deliberate time, after a failure with its propulsion system.

Artist’s view of Integral

It’s this poor propulsion system that meant a usually rectifying Safe Mode was ineffective on this event. With the mode now disabled, the Control Team are engaged on a brand new automated rescue sequence that ought to mimic most of the operations carried out after this anomaly, solely a lot sooner.When the propulsion system failed, the group realised they’d have to study to manoeuvre the four-tonne satellite tv for pc utilizing its extremely delicate response wheels alone, to dump power at common durations and counteract forces on the spacecraft, together with the light shove from the Sun’s gentle. It was an answer that had by no means been tried earlier than.“I didn’t believe it was possible at first. We checked with our flight dynamics colleagues and the theory indicated it would work. After doing a simulation, we tested it on the spacecraft. It worked,” explains Richard.“Thanks to our quick-witted team and the help of experts from across industry, Integral lives on. Almost two decades old, it is far outliving expectations for what was meant to be a five-year mission.”Listen to Richard recount the story of Integral’s earlier rescue and improve and the superb teamwork that saved the mission, within the newest episode of the ESA Explores Space Operations podcast. 

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